The prior art offers a number of methods for aligning microelectronic devices (hereinafter “devices”) to sockets, such as, for example, test sockets.
As shown in FIG. 1, according to a passive alignment method, a microelectronic device in the form of a package 100 is passively aligned with guide walls 102 on a socket 104. Such a passive alignment method relies on the clearance between socket guide walls 102 and edges 106 of package 100 in order to effect the alignment of contact pads 108 on the package 100 to contact pins 109 of the socket 104. However, disadvantageously, a reliance on the clearance mentioned above, in addition to a reliance on a control of manufacturing variations inherent in the dimensions of guide walls 102 and device edges 106 negatively impacts the alignment accuracy between contact pads 108 on the package 100 and contact pins 109 of the socket 104. In addition, disadvantageously, because of significant positional variations of contact pad arrays from device to device, the passive alignment method is not applicable to device contact pads smaller than about 12 mils.
Another known socket alignment method, such as shown for example in FIGS. 2a and 2b, uses a non-calibrated active alignment process to align package 200 to a socket 204. According to such a method, an alignment mechanism includes spring-loaded socket guides 202 (FIG. 2a) to push package 200 against socket datum 204 (FIG. 2b), and this in order to eliminate package positioning errors arising from the clearance gap between package edges and the socket walls, as described above with respect to FIG. 1. The above enhances alignment accuracy to about 10 mils, but is still largely inapplicable to the alignment of devices having contact pads smaller than about 10 mils.
Vision-based active alignment systems further exist as part of test handling equipments in order to allow a more precise alignment of a device to a corresponding socket. As seen in FIGS. 3a and 3b, a vision-based active alignment system 300 for each socket contactor or socket 310 includes a handling chuck 312 that is adapted to hold and move a device in the form of a package 314, the package having an array of contact pads 316 thereon. A camera 318 of the test handling equipment shown is positioned to acquire data in the form of an image of the array of contact pads 316 on the package 314. A control system 320 is then used to determine a positioning error between the array of contact pads 316 and the known position of an array of contact test pins 322 on the socket 310. The position of the array of contact test pins 322 may also be determined via camera imaging. The control system 320 then moves the handling chuck 312 as a function of the determined positioning error in order to align the array of contact pads 316 to the corresponding array of test contact pins 322 on the socket 310.
However, mechanical, calibration and other tolerances in the use of the above system disadvantageously limit positional accuracy to about 40 microns. The above leads to a socketing alignment accuracy of about 7 to about 8 mils.
The prior art fails to provide an alignment mechanism and method adapted to allow the alignment of a microelectronic device having contact pads measuring less than 7 mils, such as contact pads measuring about 5 mils.
For simplicity and clarity of illustration, elements in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Where considered appropriate, reference numerals have been repeated among the drawings to indicate corresponding or analogous elements.